Means for producing magnification with a four electrode valve and circuits therefor



May 31, 1932. E w B GILL MEANS FOR PRODUCING MACNII ICATION WITH A FOUR-ELECTRODE VALVE AND CIRCUITS THEREFOR Filed Nov. 25, 1-925 Fly. 1

INVENTOR E.W. B. GILL BY W ORNEY Patented May 31, 1932 UNITED STATES PATENT OFFICE? ERNEST WALTER BRUDENELL GILL, OF OXFORD, ENGLAND, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE MEANS FOR PRODUCING MAGNIFICATION WITH A FOUR ELECTRODE VALVE AND CIRCUITS THEREFOR Application filed November 25, 1925, Serial No. 71,492, and in Great Britain November 27, 1924.

With magnification by a three electrode valve, the magnification obtainable by the resistance drop method is limited by the physical constants of the valve which determine its limiting M value, but with a four tension voltage, a magnification is obtained which increases in certain cases theoretically, without limit, with theincrease of the resistance in the lead to the inner grid, since (above a critical value of its potential) the current to the inner grid is substantially independent of its potential.

According to the present invention the inner grid, which is employed as an output anode, is charged through a choking coil, whereby very high magnification is obtained.

It is known that if in a four electrode valve the plate be kept at a fixed positive potential relative to the filament, and the voltage impulses to be magnified are applied to the outer grid, then, if a fairly high potential be applied to the inner grid, this last may be regarded as the main output anode and the current therefrom will vary with variations in the voltage applied to the outer grid. The relationship between inner grid current (191) and outer grid potential (V92) is shown graphically in Figure 1, each curve of which connects 191 with V92 for a different value of inner grid potential (V91). It will be seen that the curves shift away from the origin as V91 is increased, but that equal increments of Vgl do not result in equal amounts of shift. As V91 gets greater and greater, the amount of shift for successive equal increments becomes less and less.

I have found that wit-h certain types of valves and values of V571 between certain limits, the curves substantially coincide, so that magnification is independent of V91.

It will be apparent that, since all the curves have substantially the same slope, the effect is as though the M value of the valve were increasing at a very rapid rate. If, therefore,

.. a four electrode valve be employed as a magnifier by the resistance coupled method, the

inner grid being charged through a resistance R, then by increasing R and Vgl, a very high degree of magnification may be obtained. This however, is not of very great practical advantage, since the value of Vgl necessitated is inconveniently large.

According to the present invention, I provide a choke coil through which the inner grid is charged. This arrangement enables a high degree of magnification to be obtained without employing an inconveniently large high tension battery, and, in the limiting case of a perfect choke coil, whose effective resistance is infinite, a very large magnification may be obtained.

I have found that the overall magnification tends to approximate to an inverse function of the frequency, and that it may conveniently be made very high for audio frequencles.

I have found that the overall magnification depends also upon the value of the capacity in shuntwith the choke coil. In practice each capacity would comprise the capacity of the intervalve coupling condenser and the interelectrode self-capacity of the valves concerned.

The manner in which the present invention is carried out will be better understood from the following description taken in connection with the drawings in which:

Fig. 1 shows diagrammatically the relationship of the inner grid current to the outer grid voltage for various values of the inner grid voltage.

Fig. 2 is a diagram of the system connected for a two stage audio frequency amplifier.

Referring now to Figure 2, which shows a circuit diagram for a two stage audio frequency amplifier, the first valve A is of the four electrode type, and the second valve B is a triode in cascade therewith.

1 is a choke coil through which the inner grid 2 of the valve A is charged, and 3 is a condenser through which the amplified impulses are applied to the grid of the triode B. 4 is the usual high resistance or grid leak for the triode.

It will be observed that with this arrange ment the choke coil 1 has in parallel with it b-al (through the condenser 3) the grid leak 4. This, coupled with the fact that the choke coil is never a perfect one, tends to remove dependence upon frequency so that in practice there is substantially no frequency distortion.

A circuit which is similar in general may be employed, in which the four electrode valve functions as a high frequency amplifier and or as a rectifier.

I may also employ a plurality of four electrode valves arranged in cascade.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. In an amplifying system the combina tion of a four electrode vacuum tube having an anode, a cathode, and two grid electrodes, an input circuit associated with one of said grids and said cathode, a direct current source connected between said anode and cathode, a choke coil associated with the other grid and the cathode of said four electrode vacuum tube, and a three electrode valve having its input circuit capacitively coupled to said last named grid.

2. In an amplifying system the combination of a four electrode vacuum tube having an anode, an inner and outer grid surrounding a cathode, an input circuit connected between said outer grid and said cathode, an output circuit connected between said inner grid and said cathode, a triode, an input circuit therefor a portion of which is common to the output circuit of said four electrode tube, and a choke coil and a source of power associated with the inner grid of said four electrode tube.

3. The method of amplifying electrical impulses with a four element tube having an anode, a cathode and inner grid and an outer grid which comprises impressing said impulses upon the outer grid of said tube, charging the anode of said tube, charging the inner grid of said tube with a potential higher than that applied to the anode, substantially excluding alternating current from the charging circuit and impressing the potential 0 variations of said inner grid upon the input of an amplifier to regulate the output of said amplifier. I

4. A vacuum tube relay comprising a four v, electrode tube having a cathode anode and two grid electrodes. an input circuit connecting one of said grids to said cathode, means for connecting said anode directly to a source of direct current, means including a choke coil and a source of direct current of relative- 1y high potential connected between the other grid and the cathode, a triode tube and means including a capacity having one end connected to the last mentioned grid and to the choke coil, for coupling said grid to the input circuit of the triode tube.

5. In a system for amplifying, the combination of a four element tube having a cathode, an anode and two grids between said cathode and said anode, a source of current connected between said anode and said cathode, a source of current of higher potential than said first named source and a choke coil connecting one of said grids to said cathode, an input circuit connected between the other grid and the cathode and a second vacuum tube the input circuit of which is associated with said first named grid cathode circuit for cascade amplification.

6. In an amplifying system the combination of a four element tube having a cathode, an anode and two grid electrodes between said cathode and anode, means including a direct current source connected between said anode and cathode for charging said anode,

means including a direct current source of higher potential than said first named source and a choke. coil for charging one of said grids, and a second thermionic tube having input and output circuits, the input circuit of which is capacitively associated with said last e named grid whereby the potential variations in the output circuit of said second named tube is controlled by the potential variations of said choke coil charged grid acting on the input circuit of said last named tube.

7. In an amplifying system an electron discharge device having a cathode, an anode and two grid electrodes interposed between said cathode and said anode, an input circuit associated with the outer grid, a current' source directly connected to said anode and to said cathode, and a current source of higher potential than said first named source connected to said inner grid through a choke coil whereby a small variation of power in the input circuit will cause a large variation of power in the inner grid circuit.

8. In an amplifying system, a four element tube having a cathode, an anode and two grid electrodes interposed therebetween, an input circuit associated with one of said grids and said cathode, a power source associated with said anode and said cathode, an output circuit associated with the other of said grids and said cathode, a choke coil and a source of power for charging said last named grid, and a three element tube having grid cathode and anode electrodes and a grid cathode circuit which is associated with said output cir-' cuit for cascade amplification.

9. In a system for magnification, a four element tube having a cathode, an anode and an inner grid and outer grid, an input circuit connected between said outer grid and said cathode, a source of high potential applied directly to said anode, an output circuit associated with said inner grid, and a choke coil and a source of potential for charging said inner grid whereby the coeflicient of magnification of the tube is independent of the potential of the inner grid.

10. In a vacuum tube relay a four electrode tube having a cathode, an anode and outer and inner grid electrodes, a source of direct current for charging said anode, an input circuit connecting said outer grid to said cathode, an output circuit connecting said inner grid to said cathode, a choke coil and a source of direct current for charging said last named grid, a capacity in said output circuit, a second vacuum tube having input and output elements, and an input circuit. for said last named tube connected to said capacity Whereby the potential variations in the output circuit of the first named tube are impressed on the input circuit of the last named tube.

ERNEST WALTER BRUDENELL GILL. 

